Correlation between miR-204 expression and PAH severity. (A) miR-204 is decreased in human, mouse, and rat PAH lungs. qRT-PCR analysis of miR-204 expression in human lungs with PAH (n = 8), mouse lungs with hypoxia-induced pulmonary hypertension (n = 6), and rat lungs with MCT-induced pulmonary hypertension (n = 5) compared with human (n = 8), mouse (n = 10) and rat (n = 5) control (Ctrl) lungs. (B) miR-204 is mainly expressed in the distal PAs. qRT-PCR analysis of miR-204 expression in several rat organs with MCT-induced pulmonary hypertension (n = 5) compared with control rats (n = 5). (C) miR-204 down-regulation correlates with PAH severity. qRT-PCR analysis of miR-204 expression in the lungs from healthy subjects (n = 8) and from patients with varying severity of PAH (n = 3), in mouse lungs with varying severity of hypoxia-induced pulmonary hypertension (n = 3), and in rat lungs with varying severity of MCT-induced pulmonary hypertension (n = 3) compared with control animals (n = 5 for both rats and mice; n = 3 experiments per patient or per animal for each pulmonary vascular resistance [PVR] or mean pulmonary arterial pressure [PAP] listed, and significance is compared with control group). In all experiments, the level of miR-204 is relative to the control RNA U6. Data are expressed as means ± SEM (*, P < 0.05; **, P < 0.01; ***, P < 0.001).